Carrier telegraph circuits



@et Z i923. lgf v R. W., DEARDRFF CARRIER TELEGRAPH CIRCUITS Filed -Capel. 1920 4 sheets-sheet 1 INVENTOR BY 7M K ATTORNEY WWW/MW# lR. W. DEARDORFF CARRIER TELEGRAPH CIRCUITS Filed oct. 21', 1920A 4 sheets-sheet 2 @ci 2, w23. I l www@ y R. DEARDORFF CARRIER TEIJEGRAPH CIRCUITS Filed om. 21, 1920 4 Smets-sheet 3 E is BYa

L ATTRNEY @et 2 i923.,

` R. W. DEARDORFF :CARRIER TELEGRAPH CIRCUITS Filed Oct. 2l. 1920 4 sheets-Smm 4 lNvENToR I ATTORNEY ence to the Patented @et 2, l923 LAQSA umTan sTaTes raTranT crema.

i RALPH "WARNER DEARDORFF, OF BROOKLYN, NEW YORK, ASSGNOR T0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A

CORPORATION -OF NEW YORK.

CARRIER TELEGRAPH CIRCUJITS.'

Application led October 21, 1920. Serial No. 1&721

To aZZ whom t may concern.'

Be it known that I, RALPH W. DEARDORFF, residing at Brooklyn, in the county of Kings and State' of New York, have invented certain Improvements in Carrier Telegraph Circuits, of which the following is a specification.

This invention relates to signaling systems and more particularly to signaling systems in which telegraphic signals are transmitted by means of carrier currents.

@ne of the objects of the invention has reference to the. provision of means for associating a local telegraph circuit or loop with the channels of a carrier telegraph system.

Another object ofthe invention has reference to the provision of means for associating an ordinary telegraph circuit or loop with the channels of a repeater arrangement for a carrier telegraph system.

Another object of the invention has referprevention, in a system of the character above described, of the response of the receiving relayof la carrie-r channel when signals are being transmitted from the local circuit or loop to the transmitting carrier channel, an auxiliary winding of the relay being preferably employed for this pur- Another object of the invention has reference to the provision of two polar relays associated with the subseribers loop for transmittinor purposes, one of the polar relays controlling the carrier transmitting channel,

the other relay serving to render the receiving relay inoperativewhen signals are being tranmnitted.

Another object of the invention is to provide a transmitting and receiving circuit in connection with the channels of a carriersys- 'tem in which the low frequency loop 'circuit is provided with a balanced polar relay at each end, with such an organization of sources of current that the polar relays may be operated by changing the current flow in the loop circuit. which result may beaccomplished either by opening and closing the loop'circuit or' by changing the polarity of the battery connections.

Another object of the invention is to provide an arrangement for associating a local telegraph circuit or loop with the channels of a earriersystem in which the contacts'of the receiving relays and windings of the will be clear from the following description when read in connection with-the accompanying drawings, Figures l and 2 of which constitute circuit diagrams lillustrating two methods of associating a loop circuit with the channels of a carrier system in such a manner as to operate upon a half duplex-basis, and Figs. 3, 4 and 5 of which constitute. circuit diagrams illustrating three different methods of associating loop circuits with the channels of a repeater for a carrier telegraph system. l

Referring to Fig. 1, ML designates the main transmission line over which telegraph signals may be transmitted by means of carrier currents. A transmitting channel TL and a receiving channel 'RL are associated with the main line ML. In order to render these two channels substantially conjugate the channel RL is associated with the line. ML through a balanced transformer arrangement l() of well known construction, and. an artificial line or network MN is provided for'balancing the main line. The transmitting channel TL Vis provided with an amplifying arrangement TA of any well known constructionsuch as,.for instance, a vacuum tube amplifier adapted to amplify carrier frequencies. rent G is also'associatedwith the transmitting channel. lhis source may be any known means for supplying alternating current of the desired frequency, as. for example, a vacuum tube oscillator. Signals may be transmitted by interrupting the carrier frequency through a short circuit connection 11.

The receiving channel includes an amplifying apparatus RA similar to the vamplifying apparatus TA in the transmitting channel and a detecting arrangement D. The detecting arrangement may be of any known character such as, for instance, a vacuum tube detector, having one winding 12 of a polar receiving relay R in its out produces an effect in the detector in a well lmown manner so that when' carrier oscillations are not impressed upon the grid no current flows in the output' circuit through the winding 12 of the relay. For each train of carrier oscillations however, a pulse ot direct current ilows through thev winding 12. An -auxiliary @winding 15 energized by a direct current source 16 is provided for biasing the armature of the polar relay in a direction opposite to the pull due to the pulse of current flowing through the winding v12.. rll`he current through the winding 15 is adjusted so that the pull due to the windin 15 is but half as great as that due t0 tithe signal pulse flowing through the winding 12. rlhe net effect of the windings 12 and 15. is that normally with no carrier transmitted the armature 17 is held against its lower contact but when a train of carrier oscillations is received the pulse through the winding 12 the opposite direction which when superimposed upon the pull due to the winding l'gives a net opposite direction equal to that normally appliediby the winding 15. This permits of a strictly polar relay action under the control of direct currents.- The winding 13 inductively associated with the output circuit of the detector produces a kick at the beginning of each signalpulse to assist in shifting the armature to its marking position and another kick at the end of each signal pulse to assist in shifting the armature toits spacing position.

I L designates an ordinary telegraph circuit or subscribers loop which is arranged to serially include one w'inding 18 or" a polar transmitting relay T, and 'the contacts of the receiving relay R. A second winding 19 of the polar relay 'll is included in a balancing circuit N for the loop L. rThe loop L may include the usual transmitting key and receiving sounder at the subscribers station. A. divided battery B is serially included in the loop circuit in such a manner that the two halves of the battery are series aiding with respect t0 the winding 18, but with the armature 17 of the receiving relay on its upper Contact, only current due to the upper half of the battery Hows through the winding 19, and with the armature 17 on its lower contact only current due to the lower halt of the battery flows through winding 19. rllhe winding 18 is therefore the effective winding of the transmitting relay with the loop closed so that a circuit is completed for the .sounder relay 20. llt the loop be interrupted or it the receiving relay R be operated to shift its contact to its lower position, no current will tlow through the upper winding 18 for Vin the former case the circuit is open and in the latter case mutually opposin potentials are applied to the terminals ot 51e winding 18.

'in circuit with said Winding,

pull in the battery meegaan rlhe lower winding 19 therefore becomes edective to shift the armature of the transmitting relay so as to close the short circuit connection 11 and open the lcircuit of the sounder 20. rllhe' sounder 20-,controlsv the circuit of an auxiliary 'winding -21'with a receiving relay R and connects battery 16 ducing a pullin a direction opposite that due to the winding 15 and of enough greater magnitude to overcome the vpull due to the combined action of windings 15 vand 13.

, rll`he operation is as follows:

therefore pro- 1n the normal' condition of the circuit, I

when signals are not being transmitted, the carrier frequency generated by the generator G is transmitted continuously over the mainline ML to the distant station. Similarly, it the distant station is not signaling, the carrier frequency assigned to the receiving channel illustrated is transmitted from the distant station over theA main line into the receiving channel RL. 'llhe frequency thus continuously transmittedoperates through the detector D toproducea steady flow of direct currenththrough the windmg 12, producing a pull uponthe armature 17, tending to hold it against its up.- per Contact with a force twice as great as that of the direct current flowingv through the winding 15 which tends to pull itto its lower contact. With the armature 17 against its upper contact, current flows from the grounded point of the divided battery B, through the upper half of said battery,

through the sounder S, over the upper conloop L through the lower half ot batte-ry E to ground. Since current from the `upper half of battery B flows throughl the winding` 19 and current from both halves ofthe flows through the winding 18, the

upper winding 18 of the transmitting relay 'l is effective to hold the armature 23 of the transmitting relay against its upper Contact, maintaining the sounder 20 energized. lf now the subscriber in transmitting a signal, opens lthe loop circuit L by means of a key (not illustrated) no current lows through the winding 18 while the current flowing through the winding 19 over the path already described causes the transmitting relay to shift its armature 23, opening the circlnt of the sounder 20 and shortcircuiting the generator Gr through the conductors 11. rlhe release ot the sounder 20 closes the circuit from battery B through the winding 21 of the polar receiving relay R. and causes current to dow through said winding to produce a pull upon the armature 17 in such a direction as to hold the armature against its upper contact, notwithstanding the pull due to the winding 15. Consequently, should the current flow through the winding l2 be interrupted due to a received signal. the armature 1T would not respond to the received signal and the sounder in the loop would not be affected. The short-circuiting of the generator G by the contact 11. as already described.v results in the interruption of the transmission ot the carrier frequency from the generator G through the amplifier TA to the main line ML, the carrier frequency being diverted through the shunt path. The receiving apparatus at the distant station will respond to the interruption of the carrier frequency and record thesignal.

Should the carrier frequency transmitted from the main line ML to the receiving' channel RL be interrupted at the distant station in transmitting a signal, the direct current flowing through the winding 12 would cease to flow, owing to the fact that the vacuum tube detector D is so adjusted that current flows in its plate circuit only when the carrier frequency is applied to the grid. Owing to the interruption of the current flowing through the winding 12, the winding 15 becomes effective to pull the armature from the upper contact of the relay R to the lower contact thereof. The armature is given additional impetus in this direction by the momentary current induced through the transformer' 14: in the winding 13. As soon as the armature is shifted, current flows from the grounded midpoint of battery B, through the lower half of said battery, over the lower contact of t-he receiving relay R and through winding 19 of the transmittincV relay Tand the balancing net-work ha to ground. No current flows through the upper winding 18 of the transmitting relay as the loop is short-circuited over the lower contact of the receiving relay. The current flowing through the winding 19 of the transmitting relay T is in the direction opposite to that which normally flows therethrough and consequently, the lower winding is so energized as to hold the armature 23 against its upper contact. Consequently, the received signal can not be transmitted back through the transmitting channel to the main line ML. rl`he short-circuiting of the loop L causes the Sounders therein to be deenergized with cach interruption of the received carrier frequency so that the Sounders record the transmitted signals.

f, while signals are being received in the loop L, it is desired to transmit a break signal to the distant sending operator, in order that signals may be transmitted in the reverse direction. the transmitting key 1n the loop L will be held open. thereby causing the transmitting relay I`l` to shift its arn'iature 23 to its lower contact. The shortcircuiting of the generator (i interrupts the 'transmission of the carrier frequency to the The effect of the Vbreak7 signals at the distant sendingstatin may be understood from a consideration of thc effect produced by transmitting a break signal from the distant station to the station illustrated, when the operator at the latter station is sending. rl`he interruption of the carrier frequency received by the channel RL. due to the breaki signal, causes the detector D to interrupt the current'flow through the winding 12 of the receiving relay ll. It at that moment. the loop L is opened to transmit a space signal. the armature 23 of the transmitting relay Tl will have opened the circuit of the sounder 2t) so thatthe winding 21 of the receiving relay will be energized to hohl the armature 17 in its upper posit-ion. As soon as the loop is again closed, however, to transmit a dot or a. dash, the circuit-of sounder 20 will be again closed by the armature 23 of the transmitting relay, and the current flow through the winding 21 will be interrupted. As current flows neither through the winding 12 nor the winding 21, the winding 15 is effective to pull the armature 17 of the receiving relay to its lower contact, at which position it will remain during the continuance of the break signal.` As the loop is now shortcircuited, the operator, who is attempting to transmit over the loop L will recognize that ya break signal has been'sent from the distant station by reason of the fact that the sounder (not illustrated). in the loop, does not follow the transmitting key.A

A slightly modified arrangement is shown in Fig. 2. The circuit in this figure differs,

from that illustrated in Fig. 1, mainly in the details of the transmitting and receiving relays. In this instance, the t `ansmitting relay arrangement comprises two polar relays l and l` cach having windings in the circuit of .the loop L and in the balancing circuit N. The windings of the two polar re-- lays are each connected in parallel to the junction point 22. The armature 23 of the polar relay P controls the circuit of the sounder 20 and short-circuitsthe connection 11 of the gene 'ator G, while the armature.

Q3 of the polar relay P controls the auxiliary winding 24 of the receiving relay R, to prevent response of the receiving relav to llO received signals while si nals are being transmitted from the loop Separate polar relays are used as illustrated for the reason that commercial polar relays are ,usually only provided with one armature and two polar relays therefore become necessary to perform all of the functions demanded. .The battery7 connections over the amature 17 oi' the receiving relay R'to thewindings of the polar-relays P Iand P of the loop L, are similar to those illustrated in Fig. 1, so that the armatures 23 and 23 vare normally held in their upper position due to the fact that the current flow through the upper windings of the polar relays is greater than that through the lower windings.

rlhe receiving relay R comprises a main winding 25 and an auxilia winding 24, the main winding 25 being inc uded in the output circuit of the vacuum tube detector D. An inductance 26 is bridged across the out- .put circuit to form a by-pa-th for the direct current component of the detected signal pulses, while the condenser 27 permits the alternating current component to pass through the main winding 25 of the relay lt while excluding the direct current component. If it is desired that ya certain portion of the direct current component be permitted to pass through the winding 25, the condenser 27 may be shunted by the resistlance 28. The armature 23 of the polar transmitting relay P whichv controls the energiz'ationof the winding 24 of the receiving relay R, permits current to flow from the upper half of battery B, through the winding 24 when said armature is in: its upper posltion. Current therefore vHows through said winding of such strength and in such direction as to produce a pull tending to draw the armature 17 to its lower contact. The pull due to the direct current passing through lthe resistance 28 to the winding 25, however, is twice as great in the opposite direction as long as the carrier fre-l quency transmitted to the receiving channel yao RL is heinoreceived. The Windin 24 is onlyefective to shift the armature 1 to its lower position when the received carrier frequency is interrupted in the transmissie i ofsignals. 'llhe Ialternating component of the received signals causes kicks at the beginning and-end of each signal impressed in such direction through the winding 25 as to shift the armature 17 from one positionto the other. `When the armature 23 of the polar relay P is in its lower position, current flows ,from the lower half of the battery B through winding 24 of the receiving relay R in the opposite direction so as to hold the armature 17 against its upper contact regardless of the received impulses through the winding 25;

rllhe operation is as follows: ln transmitting, the operation of the key, by openthe former short-circuiting the generator Y raeeeea ing the loop, causes, current How 'only throu h the lower windings of the polar'relays A and P so that the armatures 23 and 23 are shifted to their alternate position,

the circuit of the sounder S 'as and openin he armature .23 on shifting to in Fig. 1.

yits alternate contact, interrupts the supply of biasing current to the vwindingw24-of the receiving relay R and causes current to flow through said winding in the other direction from the other -half of battery B, thereby Afrequency causes the cessation ofthe current flow through the Winding 25, and the armature 17 is shifted to its alternate contact by the current flowing from the upper half. of battery B through the winding 24. The shifting of the armature 17 to its alternate contact connects mutually opposed sources to the ends of the loop L so that no current flows in the loop and the sounders in the loop respond to the interruption of the carrier frequency. While no current flows through the upper windings of the polar Arelays P and P', the current through the lower'windings is in the direction opposite to their normal flow, so that the lower windings open and hold the windings 23 and 23 against their contacts, thereby preventing received signals from being transmitted back to the main line.

In transmitting a break signal, the opening ofthe' loop operates the polar relays P and P as before to interrupt the carrier vfrequency by short-circuiting the generator G, and to change the direction of the flow of current through the winding 24, thereby preventing the relay R from responding to received signals. lf, on the other hand, the station illustrated is sending and a break signal should be received, the interruption of the carrier frequency in the receiving channel RL would result in the cessation of the current flow through the winding 25 of thepolar receiving relay so that the armature 17 would be shifted to its alternate contact by the winding 24, and due to the 'mutually opposed sources at the ends of the loop, 11o-*current would flow in `serving that the local sounder no longer followed the operation of the transmitting key.

Fig. 3 illustrates an arrangement for a'ssociating the subscribers loop with the channels of aV carrier telegraph repeater in such manner that 'the transmission of signels to and from the loop lwill be upon a iat , relays iacaaea half-duplex basis. Referring to Fig. 3, MLE and MLW designate transmission line sections os r which carrier currents may be transmitted. A repeater interconnects said sections, said apparatus comprising receiving channels BLE and RLW associated with the line sections, and transmitting channels TLE and TLW, likewise associated with the line sections. Balanced transformers 10 and l0 and artificial lines or networks vNME and NMW are provided as indicated for the purpose of rendering each transmitting channel and the corresponding receiving channels substantially conjugate. The receiving channels include amplifying arrangements RAE and RAW respectively, these arrangements being similar to those de-v scribed in connection with Fig. l. Similarly, the transmitting channels include amplifying arrangements TAE and TAW of like construction.

In order to provide a direct path for the amplification of carrier currents from east to west, the output circuit of the amplifier RAE is connected through conductors 29 to the input circuit of the amplifier TAW. In a similar manner, a path for amplification from West to east is provided by connecting the output circuit of the amplifier RAW with the input circuit of the amplifier TAE through conductors 30. In order that carrier signals transmitted through the repeater from one line section to the other may be received in the local loop L, detectors DE and DW are associated with the receiving channels RLE and RLV respectively, polar relay arrangements RE and RW, similar to the polar relay R of Fig. 2, being included in the output circuits of the detector, and controlling the loop circuit by their contacts.' In order to transmit signals from the loop to the line sections through the repeater apparatus, pairs of polar transmitting relays PE--PE and PVV--PW respectively, arel provided, these polar relays being similar in construction to the relays P and P of Fig. 2. The loop L is connected from one pole of the divided 4battery B to the terminals 3 1 and 32 of the transmitting polar relay arrangements so that the windings of the two sets of polar for transmitting in opposite directions will be connected in parallel with respect to the loop, and a common balancing network N is likewise connectedl to the terminals 33 and 34 of the two sets of polar relays so ythat the two sets will be in parallel with'respect to the balancing circuit.

l Likewise the junction points 35 and 36 of the titl polar relay sets are joined together through a contact 37 to a common conductor 38, eX- tending over the normal contacts on the receiving relays RE and RW to the pole of the divided battery B, opposite :to that connected to the other end of the loop. will Eil be noted that the normal contacts of the receiving relays are connected in series in the circuit of the loop so that signals received throug either line sectionwill be repeated to the loop while the transmitting relay sets are connected in parallel with respect to the loop, so that signals from the loop will actuate both relay sets to repeat the loop signals to both main line sections.

In order to transmit the signals from the loop to the line sections, the short-circuit connections 11 and l1 are controlled by the armatures of the polar relays PW and PE so that when the short-circuit connections are closed, the carrier frequencies which are normally transmitted in both directions over the circuits 29 and 30, are prevented from transmission. to the amplifiers TAE v and TAW, thereby interrupting the carrier frequency transmitted from each line section to the other. The contacts of the relays PE and PYV ings of the receiving relays RE and RW in a mannner similar to thatdescribed in connection with Fig. 2.

The operation is as follows: Normally, in the absence of signals, Continous transmission form east to west takes place over the amplifying path through the receiving channel RLE, amplifier RAE, conductors 29, amplifier T AVV and l TLW. Likewise transmission. in the opposite direction flows into the receiving channel RLV, through the amplifier RAW, over conductors 30, through the amplifier TAE and over the transmitting channel TLE .to the line section MLE. These paths-are high frequency amplification paths, whereby the carrier frequencies are amplified in their cairier state without detection, and the signals will be transmitted from one line section to the other by the interruption of the carrier frequencies. There the repeater is operating on a half-duplex basis, signals will be transmitted in only one direction at a time. Consequently, interruptions in the carrier frequency will occur in only one of the amplification paths, the transmission of the carrier freqency through the other path being constant.

Signals maybe transmitted from the loop L to both line sections MLE and MLW simultaneously by interrupting the loop 'by means of a key, so that no current flows through the upper windings of the two sets of polar transmitting relays. The lower windings are therefore energized, Shifting the armatures to their lower contacts Aand closing the short-circuiting connections 11 and 11, whereby the transmission of carrier frequencies through the oppositely directed amplifying paths is interrupted, the Sounders SE and SW being caused to re* spoiid at thiZ same time. The armatures of the polai :elaysPE and PVV, by changing transmitting channel,

control the auxiliary windsets.

f main the direction of current flow through the auxiliary windings of the receiving relays RE and RW, hold the armatures of said relays against their normal contacts .to prevent the relays from responding to received signals.

- lf signals are being transmitted from east to west over the carrier repeater channel, including the conductors 29, the d'etec4 tor DE, in response to each interruption of the carrier frequencies, causes the receiving relay RE to shift its armature from its nor mal connection to negative battery over the contact ofthe receiving relay RW to positive battery.- Mutually opposed sources are now connected to opposite ends ofthe loop L and no current flows through the upper windings of the two ltransmitting polar relay The source connected .over the alternate contact of the receiving relay RE to the windings of the polar relays of the two sets of transmitting relays, is of such polarity that the current flowing through the lower windings of relay PE and'PE tends to hold the armatures of said relays in' their normal positions, thereby preventing the detected signals from being "transmitted back to the line' section MLE from which they came; also .preventing the transmitting relays PW and PW from short-circuiting the conductors 29 to interfere with the transmission over the line section MEE to theline section Similarly, if. signals are transmitted from west to east over the amplification path 30, the relay RW responds to shift the polarity ofthe battery connected to the conductor 38, thereby sources to the ends of the loop L to prevent all current flo'w in 'the loop. The 'current flow' through the' polarwindings of both sets of transmitting polar relays is `in such direcdetail.

tion aajto prevent the operation of the relays.- The .transmission of a break signal from the loop Eor to `the loop L will be readily understood .without further descripti'on. by reason 'of thel fact that it is similar in principle totliat described in connection with Fig. 2.: 1

Fig. 4 illustrates an arrangement similar to that. of Fig. 3 with the loop circuit connected in series with the polar transmitting relays and the contacts of the receivingrelays.v The apparatus is in general similar to that of Fig. 3,'and need not be described in rlihe essential difference in the tivo circuits resides in the fact that the loop 'L is serially connected between points 81 and 32,'while separate conductors, 38 and 39, eX- ten'd from the junction points 35 and 36 of the windings of the polar transmitting re# lays, to the armatures of the receiving relays RE and RW respectively. rl`he armatures of the receiving relays, when resting upon their normal contacts, are

connecting mutually opposed- -nel'tol the line section MEW, is

connected to positive and negativepoles of thev divided battery B, the alternate contacts of the relays beingoppositely connected to the poles of said battery so that if the armature of either relay isshifted, conductors 38 and 39 are connected to the same pole of the battery. rllwo artificial lines or networks, NE and NW, connected by metallic conductor 40, are provided for balancing the polar transmitting relay setsv with respect to the loop L.

Signals may be transmitted from the loop by interrupting its circuit so that no cury rent flows through the upper windings of either set of polar transmitting relays. The lower windings-of the two sets of polar relays operate to shift the armatures to their alternate contacts thereby openin the circuits of the Sounders SE and S` 7V, shortcircuiting the conductors 29 and 3() to interrupt the carrier frequency and change the direction of current flow through the auX-- iliary windings of the polar receiving relays to prevent the response of said `relays to signals.

Signals received from the line section MLE operate the receiving polar relay RE, thereby connecting the conductor 38 to the positive pole of the battery .instead of to the negative pole thereof. Since both conductors 38I and4 39 are now connected to the positive pole of the battery, no current flows through the loop and the Sounders in' the loop therefore release their armatures.

lt will be observed that in this operation, the direction. of the current flowing through the lower windings of the relays PE and PE was changed so that the armatures of these two relays are not shifted. lVith respect to the polar relays PW and PVV, how- 105 ever, the condition isdifferent upon interruption of the loop L. Since no current flows through the upper windings and the current flowing in the lower windings is in the normal direction, the armatures of these` `without effect, since at thetime the conductors are short-circuited, the carrier frequency incoming fromV the line section MLE to be transmitted throughthe repeater cha`n' already interrupted. t f

The operations attending 4vthe transmis sion of a break signal `-either to or from '125 the loop. willl be vobvious'"without descrip-A tion, and consequently, description thereof will be omitted. I

Fig. 5 illustrates an arrangementsimilar 'to those shown in Figs. 3 and 4 except that 130 in this instance, the system is' arranged to operate upon a, full-.duplex basis, that is, signals may be transmitted through the ear-I rier channels simultaneously in both directions. This necessitatesv the provision ot' two loops, LE and LlV, of which the loop LE is arranged to receive- ,signals transmittedthrough the repeater channel from west to east, and to transmit signals east, while the loop LV is arranged to receive signals transmitted through the repeater channelfrom east to west and to transmit signals west. rPhe `loop V is associated with the polar receiving relays PE and PE in a manner similar to that described in the, other figures, and one end of the loop passes over the contacts of the receiving relay llV. The loop LV is associated with the transmitting polar relays PV and PW', and one end of the loop passes over the contacts ot' the receiving relay RE. The various parts of the apparatus are otherwise .similar to the elements described in connection with previous figuresand neednot he considered in detail. The operation is as follows:

vSignals transmitted over the carrier channel from east to west pass into the receiving channel RLE, through the amplifie-r RAE, over conductors 29, through the amplifier TAV and4 over the transmitting channel TLV to the line section MIV. The. detector DE responds to interruptions of the carrier frequency over this channel, thereby interrupting the directcurrent flowing through the main winding of the receiving polar relay RE, so that the armature. of said relay is shifted to its lower contact. Negative battery is now connected to both ends` of the loop LlV i that no current. fiows in the loop and thc Sounders in the loop rcspond to the interruptions in the carrier frequency. The polar rela-ys PV and PW" are not actuated, however. as the current flows through the lower windings of said relays in the'direction to hold their armatures against their normal contacts. Signals may be transmitted from the loop IV by interrupting the loop. through the agency of a sending lre'y. The interruption of the loop prevents current from flowing through the upper windings ot the relays RW and RV, andthe current of the lower windings is in such direction as to shift the armatures of the relays so' that the armature of the.relay RV, by short-circuiting the conductors 29, interrupts' the transmission of the carrier frequency to the line section MV. The armature of the polar relay P'W changes the direction of current through the auxiliary winding of the receiving relay RE, and prevents the armature ot the latter relay from responding to received signals. y

Signals transmitted from the line sect-ion MLVVpass through the carrier channel. from west to east, over the receiving channel RLV, through the amplifier RAV, over conductors 30, through the transmitting ainplifier TAE in the transmitting channel TLE to the line section MLE. Interruptions of the carrier frequency transmitted over this channel cause the detector DW to interrupt the direct current fiowing through the main windings of the receiving polar relay RlV. The armature of said relay is thereby shifted -to its lower contact so tl at negative battery is connected to both ends of the loop LE. No current now flows in the loop and the Sounders therein respond to the interruptions of' thecarrier frequency.

yThe polar relays PE and PE' are prevented fromactuation, however, due to the fact that the current flowing in the lower windings is in the direction to hold their armatures against the lower contacts. l

Signals may be transmitted from-the loopy LE to the line section MLE bv interrupting the loop in the usual ."iannei". Since no current fiows through the upper windings of the polar relays PE Vand PE, when the loop is interrupted and the current flow through the lower windings of said Vrelays is in the positive direction, the armatures of the polar relays PE and PE are shifted to the lower contacts. The armature of the relay PE short-circuits conductor 30, thereby interrupting the transmission ol` the carrier frequency to the main line section MLE. The

`armature of the' )olar rela v PE changes the directionof the current flow through the auxiliarv winding of the receiving polar re'- lay INV. thereby preventing response oi the receiving relay to received signals.

.in all of the figures above described. but one set of channels is illustrated. It will be understood. however. that in practice, the system will he multiplexed so that more than one channel in each direction wil be provided. as is indicated in all ot' the figures by the parallel connections extending from the transmitting and receiving channels adjacent tothe transmitting and receiving amplifiers. lVhen the system multiplexed, it will be understood, of course. that each of the receiving and transmitting amplifiers.

schematically indicated will include two circuits for insuring selectivity between the channels. each channel fortransmitting in a given direction having assigned to it a` different carrier frequency.I i

lt willbe obvious that the general principles herein discussed may be embodied in many other organizations widely different from those illustrated. without departing from the spirit of the invention as defined in the following claims.

`What is claimed is:

'in a signaling system a transmitting carrier channel, a receiving carrier channel. a receiving relay associated with said receiv..

lill

a polar receiving relay associated ing channel, a local telegraph circuit controlled by said receiving relay, a balancing circuit for balancing said local telegraph circuit, a polar relay arrangement associated with said telegraph circuit and balancing circuit for controlling said transmitting channel, and an auxiliary winding associated with said receiving relay for preventing said receiving relay from controlling said telegraph circuit when a signal' is being transmitted over said circuit to actuate said transmitting relay. A

2. In a signaling system a carrier transmitting channel, a carrier receiving channel, a polar receiving relay associated with said receiving channel, a local telegraph circuit controlled by said receiving relay,.a balancing circuit for said telegraph circuit, a polar relay arrangement associated with said telegraph circuit and balancing circuit for controlling said transmitting channel, and an auxiliary winding arrangement associated with said polar receiving relay for preventing the latter from controlling the telegraph circuit when a signal is transmitted over said circuit to said transmitting rel lay arrangement.

3. Ina signaling system a carrier transmitting channel, a carrier receiving channel, with said receiving channel, a llocal telegraph circuit controlled by said receiving relay, a balancing circuit for said telegraph circuit, a polar relay arrangement associated with said telegraph circuit and balancing circuit for controlling said transmitting channel, an auxiliary winding arrangement associated with vsaid polar receiving relay and a circuit arrangement whereby said winding arrangement is normally energized to bias the arma ture of the polar'relay in the direction opposite to that in which it is held by its main 'winding when carrier oscillations are received insaid recevingA channel, the biasing effect being less than the pull due to the main windings, and means whereby whenI said polar transmitting relay arrangement is actuated in response to a signal transmitted over the telegraph circuit said auxiliary winding arrangement of the polar receiving relay will be energized to prevent said relayfrom controlling said telegraph circuit.

4. In a signaling system a carrier transmitting channel, a carrier receiving channel, a polar receiving relay associated with said receiving channel, a local telegraph circuit controlled by said receiving relay, a balancing circuit for said telegraph circuit, a. polar vrelay arrangement associated with said telc- K' -g'raph circuitand balancing circuit for controlling said transmitting channel, a biasing winding associated with said polarreceiving relay and so arranged that with the polar transmitting relay in normal condition currentwill low through said aux-,iliary wind- Maaate ing in such a direction as to bias the armature in a direction opposite to the pull of the main winding of said polar relay when carrier oscillations are being received in said receiving channel, and means whereby, when said polar transmitting relay is actuated in sai through said auxiliary winding in the opposite direction to prevent said'receiving relay from controlling said telegraphcircuit. 5. In a signaling system a carrier transmitting channel, a carrier receiving channel, a receiving relay associated with said receiving channel, a local telegraph circit controlled by said receiving relay, a balanc- .ing circuit for said telegraph circuit, .a pair of polar relays each having windings in said telegroph circuit and balancing circuit, means whereby one of said polar relays will control said transmission channel and means whereby the other polar relay prevents' said receiving relay from controlling the telegraph circuit when the transmitting polar relay is actuated in response to a signal transmitted over said telegraph circuit.

6. ln a signaling system a carrier transmitting channel, a carrier receiving channel, a receiving relay associated with said receiving channel, a local telegraph circuit controlled by said receiving relay, a balancing circuit `for said telegraph circuit, a pair 'of polar relays each liavingwindings in said .telegraph circuit and balancing circuit,

response to the transmission of a signal over telegraph circuit current will iiow i iliary winding'associated with said receiving relay, said winding being controlled by the other polar relay toprevent said receiving relay controlling said telegraph circuit when said transmitting relay is actuated by a signal transmitted over said telegraph circuit.

7.A In a signaling system a pair of transmission. line sections comprising transmitting and receiving channels associated with each section. a local telegraph loop, means to balance said loop at each end. thereof, a polar relay arrangement at each end of said loop having windings in said loop and said balancing means, said polar relays c ontrolling said transmitting channels, a receiving relay associated with each receiving channel, connections extending from the junction points of the windings of said polar transmittingv relays over the contacts of said receiving relays, sources of current associated with the normal contacts of said receiving relays. said sources being so poled as to be in series aiding relati l-n withv respect to the ist balancing circuit, thereby maintaining the contacts of the transmitting relays in a nonsignaling condition, means to open and close the loop circuit so that current flow through the windings of the transmitting relays included in the loop when the loop is interrupted and the windings in the balancing circuits are energized to transmit signals to said transmitting channels.V

ln a signaling system a pair of transmission line sectionsy comprising transmittin and receiving channels associated with eac section, a local telegraph loop, means to balance said loop at each end thereof, a polar relay arrangement at each end of said loop having windings in said loop and said balancing means, said pol-ar relays controlling said transmitting channels, a receiving relay associated with each receiving channel, connections extending from the junction points of the windings of said polar transmitting relays over the contacts of said receiving relays, sources of current associated with the normal contacts of said receiving relays, said sources being so poled asto bein series aiding relation with respect to the loop circuit whereby, with the circuit in normal condition, a greater current flows through the windings of the polar transmitting relays which are included in the loop than the current which Hows through the balancing circuit, thereby maintaining the contactsof the transmit-- ting relaysy in a non-signaling condition, means to open and close Athe loop circuit so that current ow through the windings ofI the transmitting relays included inthe loop is interrupted and the windings in the balancing circuits are energized to transmit signals to said transmitting channels, and

i means responsive to the actuation'of one of said lreceiving relays to connect a source of potential to the junction point of the windings of the corresponding transmitting relay, said source having a potential opposite to that connected to said junction point from the normal contact of a receiving rel-ay whereby current ceases to iiow through the loop and the windings of the polar relay at the opposite end of the loop are energized to vtransmit a signal from the corresponding transmitting channel while the current iiow through the balancing windling of the other transmitting 4relay is in such a direction as to hold its contacts in normal condition and therefore prevent the transmission lof the receivedsignal back to the line section trom which it was received.

9. In a signaling system a pair of transmission line sections vcomprising transmitting and receivingvchannels associated with each section, a local telegraph loop, means to balance said loop at each end thereof, a polar relay arrangement at each lend of said loop having windings n said loop and ,in such a direction I in' normal condition circuit in normal condition, a greater current Hows through the windings of the polar transmitting relays which are included in the loop than the current which flows through the balancing circuit, thereby maintaining the 'contacts ofthe transmitting relays in a non-signaling condition, and means responsive to the actuation of one of said receiving relays to connect a source of potential to the junction pointl of the corresponding transthe windings of initting relay, said source having a potential opposite to that connected to said junction point from the normal contact of a receiving relay whereby current ceases to flow through the loop and the windings of the polar relay at the opposite end of the loop corresponding transmitting channel while the current flow through the balancing winding of the other transmitting relay is as to hold its contacts and therefore prevent the transmission of the received signal back to the line section from which it was received. y y I 10. In a signaling system two transmission line sections at least one of which is used for the transmission of carrier currents, transmission channels associated with each line section, a telegraph loop, a balancing circuit at each end thereof, polar transmitting relays at each end of the loop having windings in the loop and corresponding balancing circuit, sources of opposite poten- .are energized to transmit a signal from the tial Vconnected to the junction points of' the j windings of the transmitting relays at each end of the loop whereby a greater current lows through the windings of the polar relays in the loop circuit than flows through the windings in the balancing circuit thereby maintaining the transmitting relays in non-signaling condition, and means to open and close .the loop, thereby interruptin ythe current flowing through the loop win ings in the transmitting relays and permitting the balancing windings to be energized to shift the armatures of the relays.

11. In a signaling system a pair of transmission line' sections for transmitting carrier current, transmission channels associated with each line section, a telegraph loop, a balancing circuit` at each end thereof, polar transmitting relays at each end of the loop lil@ having windings in the loop and corresponding balancing circuit, sources of opposite potential connected to the junction points of the windings of the transmitting relays at each end of the loop whereby a greater cui'- rent flows through the windings of the polar relays in the loop circuit than Hows through the windings in the balancing circuit thereby-niaintaining the transmitting relays in non-signaling condition, and means to open and close the loop, thereby interrupting the current flowing through the loop windings of the transmitting relays and permitting the balancing windings to be energzed to shift the armatures of the relays.

l2. In a signaling system a pair of transmission line sections for transmitting carrier current, a repeaterv arrangementfor interyconnecting the sections comprising transmission and receiving carrier channels associated with each section, means associated with each receiving channel for translating carrier currents into low frequency signals, connections in shunt with said translating means and extending to the transmitting channel associated with the opposite transmission line section for directly associating the receiving'channel of each line circuit with the transmitting channel of the opposite line circuit, a telegraph loop, balancing circuits at each end thereof, polar transmitting relays at the ends of the loop each having windings in the loop and iii the balancing circuits, and sources of current of opposite polarity connected to the junction points ofl the' windings of the polar transmitting relays.

13. ln a signaling system a pair of transmission line sections for. transmitting carrier lcurrent, a repeater arrangement for interconnecting -the sections comprising transmission and receiving carrier channels associated with each section, means associated with each receiving channel for Vtranslating carrier currents into low frequency signals, connections in shunt with said translating means and extending to the transmitting channel associated with the opposite transmission line section for directly associating the receiving channel of each line circuit vwith the transmitting channel of the opposite line circuit, a telegraph loop, balancing circuits at each end thereof, polar transmitting relays at the ends of the loop each having windings in the loop and in the balan'cing circuits, receiving relays associated with each receiving channel, sources of current of opposite polarity connected 'from the normalcontacts of said receiving relays to the junction points of the windings of the transmitting relays, and means whereby when a receiving relay is actuated a source of. current having potential equal to but polarity opposite to that of the source connected to the normal contact of the relay Lacasse will be connected with the junction point of the windings of vthe corresponding transmittin relay.

14. n a signaling system a pair of transmission line sections for transmitting carrier currents, a repeater for interconnecting said line sections comprising transmitting and receiving channels associated l with each section, means associated with the receiving channels for translating thel carrier currents into low frequency signals, receiving relays associated with each receiving circuit, connections extending from eachV receiving circuit in shunt with its translating means to the transmitting circuit associated with the opposite transmission line ,s ection, a telegraph loop, a balancing circuit at one end thereof, a polar relay having windings in the loop and in the balancing circuit, a connection from the junction point of said windings over the normal contact of at least one of said receiving` relays to a sourcey of current, a source of current associated with the opposite end of the loop, said source being so poled -as to Abe series aiding with respect to said first mentioned source, and means operated by said polar relay for preventing the actuation of at least one of said 'receiving relays when signals are transmitted by said loop.

15. In a signaling system a pair of transmission line sections for transmitting carrier currents, a repeater for interconnecting said line sections comprising transmitting and receiving channels associated with each section, means associatedv with the receiving channels for translating the carrier currents into low frequency signals, receiving relays associated with each receiving circuit, connections extending from each receiving circuit in shunt with its translating means to the transmitting circuit associated with the opposite-,transmission line section, a telegraph loop, a balancing circuit at one end thereof, a polar relay having windings in the loop and in the balancing circuit, a connection from the junction point of said windings over the normal contact of at least one of said receiving relays to a source of current, a source of current associated with the opposite end ofthe loop, said source being so polcd as to be series aiding with recense i channels for translating the carrier currents 'into low frequency signals, receiving relays one of said receiving relays to a source of current associated with the opposite end of 'the'loop, said source being so poled as to be series aiding with respect to said rst mentioned source, an auxiliary -Winding associated with at least one .of said receiving relays and means whereby With said signaling relay in normal condition said auxiliary Winding is energized in such a manner as to bias the armature/of the receiving relay in the direction opposite from that which it Aassumes when carrier currents are received in the corresponding receiving channel and whereby when said transmitting relay is in abnormal condition Ysaid lauxiliary Winding is so energized as to hold the armature of the receiving relay from being shifted.

In testimony whereof, I have signed my name to this specification this 19th day ot October, 1920.

RALPH WARNER DEARDORFF, 

